1. Field of the Invention
The present invention relates to sputtering apparatus and more specifically to a structure of the sputtering chamber for production of thin films of magnetic materials suitable for generating a uniform magnetic field on the substrate.
2. Description of the Prior Art
Sputtering apparatus have increasingly been used as means for forming thin films of various materials in various fields of industry. As to the sputtering method, various types have been proposed, including a dipole sputtering method in which a target electrode consisting of a film-forming bulk material and a substrate which acts as a base material on which a film is to be formed are disposed at opposite positions, and also a magnetron sputtering method in which plasma is confined by a magnetic field thus improving the film-forming efficiency to a significant degree.
On the other hand, as to the film to be formed, a number of types are known, including films of metal and dielectric materials. The present invention involves metal films, more specifically, films to be formed with magnetic materials.
When forming a film of a magnetic material by sputtering, in order to obtain a film with the required magnetic characteristics, sputtering of the material should be carried out during formation of the film by applying a parallel magnetic field, so that the magnetic domains in the film being formed can be oriented in the same direction. Since the arrangement of the magnetic domains is based upon the atomic arrangement of the atoms comprising the film material, it is desirable for the crystal structure in the formed film to be uniformly arranged over a wide range. To this end, the magnetic field which is applied in a parallel manner with respect to the surface of the substrate to be subjected to the sputtering should be uniform over as wide a range as possible. However, since uniformity of the parallel magnetic field cannot be obtained when the magnetic field strength is either too high or too low, it is difficult to align the orientations of the magnetic domains in the film being formed over the whole surface of the substrate. In view of the recent conditions in industry, however, the need to apply a more uniform magnetic field to a wider range of the substrate surface is great despite the above difficulty, since, in order to increase the production yield in the film-forming process, it is necessary to treat substrates of increased size or number.
To meet such recent requirements, manufacturers have been adopting their own individual methods. These methods basically correspond to a method which comprises generating a magnetic field by utilizing magnetic field coils or permanent magnets in the direction corresponding to the orientation with which the magnetic domains in the film should desirably be aligned, as is known, for example, from "KOHMITSUDO JIKI KIROKU GIJUTSU SHUSEI (Collection of High-Density Magnetic Recording Techniques)" (complied by Tatsuro Tsushima; published by Sogoh Gijutsu Center), FIGS. 1 and 2 (pages 167 and 197). In all the examples disclosed in this document, the density profile and the orientation of the spatial magnetic field to be generated are determined in accordance with the structure and arrangement of the magnetic field-generating source, i.e. the coils or the magnets.
FIG. 1 is a lateral cross-sectional view of an example of a conventional sputtering apparatus. Reference number 2 denotes a vacuum chamber, while reference number 24 denotes coils arranged on the lateral surfaces of the chamber 2. Within the vacuum chamber 2 are arranged a substrate heater 18, a substrate 10, a shutter 16, and a target 6, these being disposed one above the other in the mentioned order starting at the top as viewed in the Figure. The target 6 is supported by a cathods electrode 4 around which is provided an earth shield plate 22.
The substrate 10 is supported by a substrate holder 8 and magnetic plates 26 are arranged the both side of the holder 8 as shown in FIG. 1.
An example of the prior art adopts this pole plate 26 with the intention of obtaining uniform orientation and uniform density of the spatial magnetic field. However, even with this arrangement, the density profile and the orientation of the spatial magnetic field are determined in dependence on the magnetic field-generating source, i.e. the coils or the permanent magnets. Therefore, with or without the above arrangement of the prior art, it is still difficult to obtain uniform orientation and uniform strength of the magnetic field over the whole surface of the substrate.
As described above, one of the problems encountered by formation of a film of a magnetic material is the difficulty of generating a uniform magnetic field on the surface of the substrate to be formed with the film.